This is very much about personal choice, you are the one going through it, so these are just some thoughts to consider.
I'm sorry to hear that you lost your wife to breast cancer, so potentially that means you are managing this on your own. Online forums can certainly help, but having someone you can talk to at any time might also be a good support for you, so perhaps consider would it help you to have more support, beyond just medical staff. Having someone else come to appointments can be a help, as I know I have struggled to remember everything in the blur of the consultations (I'm only 51).
I'm guessing given the timescale of your diagnosis to now (13 years) and what you have said about your children that they are adults, so cancer is a reality they would have to deal with. Maybe consider don't do the big announcement, can you talk to one of your children and have them help you tell the others. It sounds like you are trying to protect them from unnecessary worry which is very admirable, but they might be a help to you too.
All the best